This invention relates to home laundry dryers and more particularly to dryers having a thermal recovery unit to decrease fuel consumption.
In a home laundry drying system, laundry in a drum is subjected to a flow of heated, dry air. When the air leaves the drum, it is still relatively hot compared to fresh air, and contains moisture absorbed from the laundry. The energy required for heating the fresh air entering the drum could be reduced, if heat from the drum exhaust could be used in the drying process, rather than simply discarded in the exhaust of the dryer.
One approach to utilizing exhaust air heat in laundry dryers has been to recirculate a portion of the exhaust into the drum, mixed with fresh, heated makeup air. A shortcoming of this approach is that it also carries the moisture from the exhaust back into the drum.
Another approach is to employ a heat exchanger to transfer heat from the exhaust air stream of the dryer to its fresh air stream. This approach has been suggested for a commercial type dryer in U.S. Pat. No. 3,859,735 to Katterjohn, Jr. The Katterjohn patent discloses an indirect heat exchanger, which is excessively large relative to a home dryer, and is mounted external to a dryer housing. Such a combination does not meet the space requirement of a home laundry dryer; therefore, nothing of this sort is marketed for home use. The enclosures of home dryers are designed to meet certain standards as to size and shape. With reliance on this standardization of size and shape, many homes are built with areas specifically sized to receive the dryer. Often these areas are constrained on the sides and backs by walls, and above by cabinetry. Thus a dryer which is to be mass produced must be in a substantially standard enclosure in order to fit the spaces provided for it in homes.
There is very little room for the addition of a heat exchanger in and around an installed home dryer; therefore, the exchanger must be small. Indirect heat exchangers, as used by Katterjohn, require a large amount of heat transfer surface area. One small enough to somehow fit in a home dryer would not have the heat transfer capacity to provide useful energy recovery.
The present invention uses heat pipes to achieve a compact, as well as highly effective, heat exchanger. This heat exchanger is used to transfer heat between the exhaust air and fresh air stream of a dryer. Importantly, ways have been found to integrate the heat exchanger into a home dryer of standard size and shape. The resulting machine has features which permit it to be operated and maintained in the confined installation conditions frequently encountered in the home. The result is a practical dryer that saves energy and can actually be used in the home.